Recently there has been much interest in providing 3-D images on 3-D image displays. It is believed that 3-D imaging will be, after color imaging, the next great innovation in imaging. We are now at the advent of introduction of 3D displays for the consumer market.
A 3-D display device usually has a display screen on which the images are displayed. Basically, a three-dimensional impression can be created by using stereo images, i.e. two slightly different images directed at the two eyes of the viewer. An example of such a device is an autostereoscopic display. In other devices images are sent in all directions and glasses are used to block certain images to give a 3D perception.
Whatever type of 3-D display is used, the 3-D image information has to be provided to the display device. This is usually done in the form of a 3-D image signal comprising digital data.
The generation of 3-D images is conventionally done by adding a depth map, said depth map providing information on the depth of the pixel within the image and thus providing 3D information. Using the depth map for an image a left and right image can be constructed providing a 3D image as disclosed in U.S. Pat. No. 6,466,207 entitled “Real-time rendering with layered depth images”. Alternatively, for example when using a multi-view autostereoscopic display, more than two views can be constructed for use in visualizing a three dimensional scene.
When the content is displayed on a display multiple views must be rendered and these are sent in different directions. A viewer will have different images on the eyes and these images are rendered such that the viewer perceives depth. The different views represent different viewing positions. However on the input data usually often one viewing angle is visible. Therefore the rendered views will have missing information in the regions behind e.g. foreground objects or information on the side of objects. Different methods exist to cope with this missing information. A solution is to add data to the signal in the form of further data layers representing parts of the 3D image that are hidden behind foreground objects. This background information is stored from the same viewing angle. There may be more than one layer of background information if in a 3D image many objects are positioned behind each other.
In such methods the content for 3D displays is stored in a multi-layer representation. This multi-layer representation captures the scene from the viewpoint of a single camera, and describes the third dimension with the help of layers. Such layers could contain transparency. Often, each layer is provided with a corresponding depth map. The layers behind the foreground layer are usually called ‘occlusion layers’.
The inventors have found that in current methods part of the occlusion information useful for accurate construction of a 3D image cannot be represented in an occlusion layer. This reduces the quality of 3-D imaging, since the missing information must be rendered by some other manner, usually leading to some sort of method to estimate the content of the missing information. However intelligent such methods may be, the missing information is generally merely an approximation of the actual content, leading to the possibility of image errors and imperfect 3-D images.
It is thus an object of the invention to provide a method for encoding 3D image data allowing an improved 3-D imaging.
It is a further object to provide an improved system for encoding a 3D image signal, a system for decoding a 3D image signal and a 3D image signal.